Biosolids, Part 1: An Orientation
This is the first of several articles exploring the use of biosolids in agriculture and residential composting products. We will start with general info about contaminants in biosolids, which contaminants wastewater treatment can and cannot remove, and begin to explore how well plants absorb those contaminants.
The series will culminate with western New York-specific information. Where are biosolids being applied locally? Which locally-available bagged compost products are made from biosolids? In which WNY towns have residents, farmers and governing bodies experienced conflict around this issue?
Biosolids: Background
At the last WNY Herb Study Group meeting I attended, herbalist Marian Prezyna of Cat’s Tail Farms gave a talk about gardening in a contaminated culture. She warned about the biosludge used to make some bagged compost products available locally. Marian recommended the documentary Biosludged, which I promptly watched.
Biosludge, or biosolids, is the solid byproduct of wastewater treatment. Wastewater is carried through sewer lines from businesses and homes to a treatment plant. Treated liquids are usually discharged into a local stream. The remaining solids “or a product developed from the solids are removed from the treatment plant for disposal or beneficial use” (NY DEC).
Biosolids are widely applied to conventional farm fields, both in New York state and nationwide. (They are not permitted in certified organic agriculture). A number of companies and municipalities sell bagged biosolids-based compost, including several made from New York state’s waste.
These products are marketed as “earth-friendly”— and they should be earth-friendly. In my opinion, the transition from outhouses-- composting waste on-site-- to defecating into clean water was a tragic waste of energy and resources. Composted manure is “black gold” to natural systems, adding concentrated organic matter to soils. Now that Americans and our infrastructure are committed to the current system, finding agricultural uses for wastewater treatment byproducts makes sense. I want to love the use of biosolids in farming and gardening.
If biosolids were “pure poop,” everything would be hunky-dory. Sadly, they are not. The EPA has identified “over 350 pollutants in sewage sludge, including metals; dioxins and dioxin-like compounds; inorganic ions; certain organics (e.g., polycyclic aromatic hydrocarbons [PAHs], semi-volatiles); polybrominated diphenyl ethers (flame retardants); pharmaceuticals; steroids and hormones; and per- and polyfluoroalkyl substances” (EPA, 2019).
How do those chemicals get in there? One problem is what residents flush (pharmaceutical drugs), pour down the drain (harmful cleaning agents, cheap “hygiene” products, etc.), and allow to run off of our lawns and vehicles (motor oil, lawn chemicals, etc.) U.S. Geological Survey scientists found that biosolids contain "relatively high concentrations (hundreds of milligrams per kilogram)" of active ingredients in common household products and drugs (USGS).
Another issue is the amount of industrial and agricultural chemicals that end up in our sewage system. We will explore this more in upcoming articles.
Wastewater Treatment Methods
In the US, wastewater treatment methods focus almost exclusively on reducing harmful bacteria. According to the NYS Department of Environmental Conservation, wastewater treatment includes these steps:
Digestion - the use of microorganisms to break down organic substances. May be aerobic or anaerobic.
Lime Stabilization - the addition of alkaline material, such as lime, to biosolids to raise the pH. This reduces odor and concentration of pathogens.
Air Drying - placing biosolids in a layer on a sand bed or paved surface. Evaporation and draining remove water.
When the intention is to market biosolids as a product, additional steps also focus on killing pathogens—not on removing harmful chemicals:
Advanced Stabilization - a process used to reduce harmful organisms to below detectable levels and produce a marketable product. Includes:
Composting - biosolids are dried and mixed with an amendment, such as wood chips or yard waste, and the mixture is allowed to decompose in an aerobic environment. This results in humus, typically used for landscaping and soil amendments.
Heat Drying - the use of a drier to remove most of the water from biosolids. In some facilities, the resultant product is in the shape of pellets, which can be marketed as a fertilizer or soil conditioning.
Chemical Fixation - a process involving the blending of biosolids with lime and, in some cases, kiln dust. It differs from lime stabilization because sufficient alkaline material is added to produce heat during treatment. The product is typically used as a liming agent on farms.
As seen above, wastewater treatment plants are not well-equipped to process industrial and agricultural chemicals, pharmaceuticals, or heavy metals in the water. Chemicals become more concentrated in biosolids as liquid is removed during processing.
Heavy Metals in Biosolids & Plant Uptake
As I began digging through regulations about biosolids, I found this statement in Biosludged to be false: 'The EPA made a rule requiring all industry to dump industrial chemical waste into the sewage system.' I found some good news instead: the federal government has implemented industrial pretreatment requirements to reduce the amount of certain contaminants entering the wastewater treatment system. These rules seem to focus on heavy metals. “Biosolids that are destined for beneficial use must be routinely tested and must meet State and federal metal standards.” (NYS DEC).
The NYS DEC reports that the concentration of heavy metals in biosolids has improved significantly in recent decades. The data below compares mean metal concentration in NYS biosolids in the 1980s and late 1990s (NYS DEC):
Unfortunately, the standards in place may not be stringent enough. Murray McBride of Cornell University reviewed the impacts of heavy metals in biosolids under the federal 503 rule, which establishes requirements for biosolids management. McBride stated that “This regulation allows the largest annual inputs and highest toxic metal concentrations in sludges that can be used in agriculture, and the largest cumulative metal pollutant loading limits that have ever been proposed in any industrialized country” (Institute for Agriculture and Trade Policy).
For those of us who add biosolids-based compost to our gardens or eat conventionally-farmed vegetables, an important question is how well plants take up heavy metals.
According to the Institute for Agriculture and Trade Policy, “most plants do not to absorb heavy metals well, but metal absorption will vary depending on soil conditions. Certain heavy metals are taken up by some plants. Spinach can absorb mercury. Many plants, including tobacco, wheat, corn, and leafy vegetables like lettuce and spinach, readily absorb cadmium. [5] Even plants that do not absorb significant amounts of cadmium can contribute a notable amount to the diet. ‘Grains and potatoes accumulate much smaller concentrations of Cd [cadmium] from contaminated soils than do leafy vegetables, but because of their greater dry weight content in most diets, can make a substantial if not dominant contribution to Cd intake by humans.’”
The Cornell University Waste Management Institute analyzed the EPA Part 503 rule in a publication called A Case for Caution. They note that the dietary risks for cadmium presumed a diet lower in vegetables than recommended by the USDA. (Cadmium is a likely human carcinogen linked to nervous system, kidney, and liver damage.) Hogs raised on corn from biosolids-fertilized soils were shown to have elevated cadmium levels. Since a grazing cow may ingest as much as 1100 pounds of soil annually, the application of sludge to grazing land may have measurable effects on dairy and beef products (Institute for Agriculture and Trade Policy). Since many contaminants of concern are fat-soluble, this is a notable risk.
How well are pharmaceuticals, agricultural chemicals, and industrial chemicals taken up in vegetable and herb plants? To what extent are these chemicals monitored?
Like other composts, wouldn't the humus in biosolids help to make harmful substances less bioavailable?
Stay tuned!
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Sources:
Biosludged documentary. Free on Youtube: https://www.youtube.com/watch?v=advyil5BkqQ
New York State Department of Conservation. "Biosolids Recycling Fact Sheet Number 1." 1999. https://www.dec.ny.gov/docs/materials_minerals_pdf/facts.pdf
United States Environmental Protection Agency. Sewage Sludge Surveys. April 18, 2019. https://www.epa.gov/biosolids/sewage-sludge-surveys
Institute for Agriculture and Trade Policy. “Sewage Sludge and Food Safety.” 1999. https://www.iatp.org/sites/default/files/Sewage_Sludge__Food_Safety.htm
United States Geological Survey. “Household Chemicals and Drugs Found in Biosolids from Wastewater Treatment Plants.” June 27, 2018. https://toxics.usgs.gov/highlights/biosolids.html
